Postmodernists believe that there is no such thing as Truth, which is different from the notion that there is no such thing as truth. I am not sure that any serious philosopher would argue against the existence of empirical truth.
Perhaps I can also help with an example. As a graduate student in physics in the early eighties I had a roommate who was a graduate student in the humanities. We often got into lengthy debate about varius matters of politics and life, and rarely could we come to closure. At one point we tried to pin down what we took as fixed versus that which was debatable (I'll try for this example to avoid using the word truth.)
It became clear that as a scientist I saw facts as fixed due to their ability to be measured and opinion to be debatable based on the facts. My friend with a postmodern bent took quite the opposite approach. He saw opinions as personal and fixed by that person, but the facts were often in doubt and therefore debatable.
We each could show clear examples from our own fields as evidence of our worldview, but the very nature of our disciplines put us at odds when we tried to match up our conclusions. Our logical progressions were so fundamentally different that if our conclusions failed to match, we had little basis for a meaningful discussion.
